Developments of recent years have produced an increasing need for systems to sense specific characteristics of various articles. For example, document authentication systems are in widespread use to sense a characteristic of a document for comparison with a registered standard. Certain forms of such systems identify documents by sensing a characteristic at a specific area or location on the document. Such systems have recognized various characteristics for identification, as characteristics involving light translucency, light reflectivity, emanating light type and so on. Exemplary forms of such systems are shown and described in U.S. Pat. Nos. 4,423,415 (Goldman) and 4,476,468 (Goldman). In relation to the present development, such systems essentially sense radiation emanating from a specified area of a document to obtain an indication of the document characteristic which is then compared with a reference to verify the authenticity of the document.
A problem typical of many systems for authenticating documents is that of locating a specific area from which the characteristic is to be sensed. For example, the observed characteristic might be the gross translucency of a specific area or window defined on the document. Consequently, authenticating the document necessitates locating the specific window. Of course, the window could be precisely marked or masked; however, such indicia is generally considered to compromise the security of the document. In some systems, it has been proposed to obscure the specific location of a characteristic window. Accordingly, for such systems to operate effectively, the window must be determined with a degree of precision for each sensing. Accurate location of the window is sometimes burdensome, particularly with respect to aged documents and systems utilizing a small window sometimes considered desirable. In general, the present invention involves a system for effectively and economically sensing a specific window of a document to provide reliable characteristic data.
In accordance with the present invention, a characteristic window is specified on a document which window can be dissected by a plurality of pixels. The system of the present invention then senses signal indications representative of the individual pixels, and the pixels are weighted so that those centrally located in the window are accorded greater significance. As a consequence, alignment on the specific window becomes less critical. Accordingly, the present development affords an improved system for sensing a discrete window (on a document for example) to provide a characteristic indication for the document that may be employed to authenticate the document.